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philh comments on Announcing the 2014 program equilibrium iterated PD tournament - Less Wrong Discussion
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Oh! You're also running your opponent playing a game against MirrorBot, not against TrollBot.
Which I still don't understand... you run SMB versus MB, time limit 10000. SMB runs MB versus MB, time limit 10000. MB versus MB times out, which meas SMB runs for > 10000 us, which means that SMB should time out and you should cooperate.
Meanwhile, SMB runs you versus MB, time limit 10000. You run MB versus MB, time limit 10000. That times out, so you time out, so SMB cooperates.
But you're defecting, which means that you're running SMB versus MB to completion, which seems like it shouldn't happen.
That does seem exploitable, if one can figure out exactly what's happening here.
Yes, it's an issue with how the "time" command is set up. Basically, timeouts are done via threads an exceptions; there's a detailed description of the "timeout" function in System.Timeout here: http://chimera.labs.oreilly.com/books/1230000000929/ch09.html#sec_timeout
However, tetronian2's "time" command catches all exceptions, which means that if multiple timeouts are nested, you can get some pretty strange behaviour.
In the TB vs SMB scenario, here's what happens:
1. The world runs TB vs SMB
2. TB runs SMB vs MB (timeout #1, 10000us)
3. SMB runs MB vs MB (timeout #2, 10000us)
4. Timeout #1 triggers an exception, which is caught by timeout #2 and handled, causing (3) to return Nothing.
5. Before the exception for timeout #2 can actually trigger, (2) finishes normally and kills the timeout thread; this means that (2) return Just Cooperate.
6. Since (2) returned Just Cooperate, TrollBot returns Defect.
I've brought this up as an issue on the GitHub issues page here: https://github.com/pdtournament/pdtournament/issues/3
I've suggested a solution that fixes this problem, but unfortunately race conditions are ultimately still present.
Thank you very much for catching this and for explaining it in detail here and on the github page; I'm going to play around with your proposed solution today and brainstorm any other ways of dealing with this.